The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Present day braking systems used with motor vehicles typically make use of a pedal travel sensor which detects a length of travel of the brake pedal when the operator presses on the brake pedal during a braking action. This detected length of movement of the brake pedal is used to determine a degree of braking action (i.e., braking force) that needs to be applied to the brake calipers of the vehicle.
FIGS. 1a-1c illustrate a conventional master cylinder in which an input rod 1 is moved axially by movement of a brake pedal 2. The input rod 1 acts on a reaction disc 3, which in turn acts on an output rod 4, when the operator presses on the brake pedal 2. The output rod 4 engages a first piston 5 within the master cylinder, which typically controls the braking action of a primary braking circuit of the vehicle (e.g., the passenger side front brake and driver side rear brake), and the first piston engages a second piston 6, which typically controls a secondary braking circuit of the vehicle (e.g., the driver side front brake and the passenger side rear brake). As seen best in FIG. 1a, a gap 7 typically exists between the face of the reaction disc and the face of the output rod. The gap may also be defined by the distance of arrow 8 in FIG. 1c. For this example, the reaction disc 3 may be considered as a part of the input rod 1, and thus the face of the reaction disc may be considered to be the face of the input rod.
This gap 7 affects the accuracy of the braking force determination when the determination is made simply by looking at the pedal 2 travel distance during a braking action. Determining the gap 7 would enable an even more accurate pedal travel determination to be made, and thus an even more accurate determination of the braking force required for a given braking action. Improved accuracy of the gap sensing may also result in an improved pedal “feel” for the operator applying the brakes. However, determining the gap 7 is not straight forward, as the gap may vary within different brake boost assist systems, and further may vary over time due to wear of various internal parts of the brake boost assist system. Still further, the distance of the gap 7 needs to be detected accurately in real time to maximize the accuracy of the brake pedal 2 travel length determination. And the mechanism for sensing the gap 7 needs to be able to operate, and to be integrated into the master cylinder, without requiring significant modification to the design and construction of the master cylinder, and without significantly increasing its expense, dimensions or weight.